1. Field of the Invention
The present invention relates to fire detectors installed in vehicles such as aircraft or trains, and especially to such a fire detector equipped with an anti-tampering measures.
2. Description of the Prior Art
In compartments of vehicles such as passenger compartments, toilets or lavatories, the heights from the floors to the ceilings thereof are generally small so there is not sufficient room for installing a fire detector. Accordingly, fire detectors provided in vehicles are generally installed in the ceiling surface of a vehicle such that most of the generally cylindrical or rectangular body of the fire detector is put into a portion above the ceiling surface and only those portions essential for fire detection such as a smoke inlet is exposed to the inside of the vehicle compartment.
To this end, the fire detector comprises a main body having a fire-detection portion and a mounting portion for mounting the main body on the ceiling surface.
As such fire detectors installed on vehicles are mounted in the low ceiling surface of various compartments as explained above, there has been frequent tampering of the fire detector, for example, covering the exposed portion of the detector body inside of compartment with paper cups or vinyl bags, etc.
Fire detectors can not detect fire phenomena such as smoke, etc., if such tampering occurs, which can lead to serious problems when a fire occurs that can not be detected during flight, movement, etc.
FIGS. 1 and 2 show a conventional fire detector 12 similar to smoke detectors currently installed on such as ceiling surface 10 of a vehicle such as an aircraft. The fire detector 12 includes a main body 14 having an ionization type fire detection portion with a structure disclosed in U.S. Pat. Nos. 4,740,703 and 4,853,544, for example, and a mounting portion 16 for mounting this main body 14 on the ceiling surface 10. The mounting portion 16 has a receiving portion 16a receiving most of the main body 14 and a surface portion 16b facing the interior of a compartment, with the main body 14 being fixed to the bottom of the receiving portion 16a by screws 18. One part of the main body 14, i.e. a head portion 14a, protrudes from a central opening portion 16c of the surface portion 16b to the compartment interior side whereby inlet portions 14b of the main body 14 can draw in smoke, etc., from the compartment in order to perform fire detection. The inlet portions 14b are provided both at the side faces of the head portion 14a as shown in FIG. 1 and on the surface thereof as shown in FIG. 2, so that both sets of inlet portions 14b can let in smoke. In order to explain one embodiment of the present invention, the head portion 14a is shown generally in the form of a regular square in a plane view shown in FIG. 2, the length of one side of the regular square being 39 mm, with the length of the diagonal line thereof accordingly being about 55 mm. The mounting portion 16 itself is fixed to the ceiling surface 10 by screws 20, and the main body 14 has a cable 22 connected thereto including a power supply line for supplying the main body 14 with power and a signal line for transimitting a fire detecting signal, etc., from the main body 14 to a fire control panel, etc., not shown.
As vehicle's users or passengers can easily reach the low ceiling surface of the vehicle, there has been fire detector tampering such as shown in FIGS. 1 and 2 such as covering it with a paper or polyethylene cups, etc., sticking chewing gum or tissue paper on the smoke inlet portions of the fire detector, or covering the portion of the main body of the fire detector exposed to the interior of the compartment with a vinyl bag. Such tampering is performed by passengers trying to sneak a smoke such as during a non-smoking flight. If the fire detector is an ionization type or photoelectric type (light scattering type) smoke detector, for example, its normal smoke detecting faculty will be ruined by such tampering.
Actually, many of the disturbances to a fire detector's faculty arise from being covered with a paper cup. Coincidentally, in some small-mouthed paper cups, for example, the inside diameter of their mouth edge are approximately coincident with the length of the diagonal of the head portion 14a of the main body 14 of the fire detector, as shown by dotted line L1 in FIG. 2. Such small-mouthed paper cups can completely cover the head portion 14a of the fire detector as shown by a dotted line C in FIG. 1. If a smoker has smoked while keeping such a small-mouthed paper cup C on the head portion 14a of the fire detector and has forgotten to remove the paper cup from its position, the fire detector can not detect fire phenomenon arising from smoke, etc., which can lead to a catastrophe when a fire occurs, especially during flying, running, etc.
FIGS. 3 and 4 show another conventional fire detector 112 such as a smoke detector installed in a ceiling surface 10, etc. of a vehicle. This detector 112 differs from the detector shown in FIGS. 1 and 2 in that a stepped portion 116d is provided around a central opening portion 116c of a surface portion 116b of a mounting portion 116 surrounding a head portion 114a of a main body 114 to enhance the inflow of smoke. As the other elements in FIGS. 3 and 4 are similar to the ones shown in FIGS. 1 and 2, they are indicated by numerals similar to those in FIGS. 1 end 2 but increased by 100.
In such a fire detector 11 2, there also occurs a problem in that the small-mouthed paper cups can be inserted entirely into the stepped portion 116d as shown by a dotted line L13 in FIG. 4 when the mouth edge of the paper cup is deformed in the form of a square.